With the Gordonstoun side missing two other internationals through injury, Phillips' leadership qualities were vital as his team dug deep to win all four of their group games in the Festival Competition, for one-term rugby schools.
Phillips started the day with a try as Stoun beat Bedfordshire's Cedars School 43-0 and then created a try for Matt Shute in the 17-14 victory over Whitgift.
His mother, the Princess Royal, and his sister, Zara, were on the sidelines for the second match, a 34-14 win over King Edward's, Bath, when he was instrumental in two tries.
He saved his best until last, sprinting 70 yards for a vital try against Lancing as his school struggled to clinch the win they needed to progress to the next round where they will face the Norfolk school, Gresham's.
His performance won admiring glances from the England flanker Tim Rodber. "He's naturally aggressive and fits in well with the pattern of back-row play adopted in Scotland," he said.
The most popular competition of its kind, now in its 58th year, brings together almost 4,500 boys from schools and colleges. The junior and preparatory schools tournaments starts today with the Open tournament beginning tomorrow.